ADIS16375 Data Sheet
Rev. E | Page 22 of 28
Bias Null Command
The continuous bias estimator (CBE) accumulates and averages
data in a 64-sample FIFO. The average time (TA) for the bias
estimates relies on the sample time base setting in NULL_CFG[7:0]
(see Table 77). Users can load the correction factors of the CBE into
the gyroscope offset correction registers (see Tabl e 59, Table 60,
Table 61, Table 62, Table 63, Table 64) using the bias null command
in GLOB_CMD[0] (see Table 90). NULL_CFG[13:8] provide
on/off controls for the sensors that update when issuing a bias
null command. The factory-default configuration for NULL_CFG
enables the bias null command for the gyroscopes, disables the
bias null command for the accelerometers, and establishes the
average time to 53.3 seconds.
Table 77. NULL_CFG (Page 3, Base Address = 0x0E)
Bits Description (Default = 0x070B)
[15:14] Not used
[13] Z-axis acceleration bias correction enable (1 = enabled)
[12] Y-axis acceleration bias correction enable (1 = enabled)
[11] X-axis acceleration bias correction enable (1 = enabled)
[10] Z-axis gyroscope bias correction enable (1 = enabled)
[9] Y-axis gyroscope bias correction enable (1 = enabled)
[8] X-axis gyroscope bias correction enable (1 = enabled)
[7:4] Not used
[3:0]
Time base control (TC), range: 0 to 13 (default = 11);
TB = 2
TC
/2460, time base,
TA = 64 × TB, average time
Turn to Page 3 (DIN = 0x8003) and set GLOB_CMD[0] = 1
(DIN = 0x8201, then DIN = 0x8300) to update the user offset
registers with the correction factors of the CBE. Make sure that the
inertial platform is stable during the entire average time for optimal
bias estimates.
Restoring Factory Calibration
Turn to Page 3 (DIN = 0x8003) and set GLOB_CMD[6] = 1
(DIN = 0x8240, 0x8300) to execute the factory calibration restore
function. This function resets each user calibration register to
zero, resets all sensor data to 0, and automatically updates the
flash memory within 72 ms. See Table 90 for more information
on GLOB_CMD.
Linear Acceleration on Effect on Gyroscope Bias
MEMS gyroscopes typically have a bias response to linear
acceleration that is normal to their axis of rotation. The ADIS16375
offers an optional compensation function for this effect. Turn to
Page 3 (DIN = 0x8003) and set GEN_CONFIG[7] = 1 (DIN =
0x8A80, then DIN = 0x8B00). These example commands also
disable the point of percussion. To enable this function as well, use
DIN = 0x8AC0, 0x8B00. This function reduces the gyroscope bias
response by a factor of at least 10.
Table 78. GEN_CONFIG (Page 3, Base Address = 0x0A)
Bits Description (Default = 0x00C0)
[15:8] Not used
[7] Linear-g compensation for gyroscopes (1 = enabled)
[6] Point of percussion alignment (1 = enabled)
[5:2] Not used
[1]
Real-time clock, daylight savings time
(1: enabled, 0: disabled)
[0]
Real-time clock control
(1: relative/elapsed timer mode, 0: calendar mode)
Point of Percussion Alignment
GEN_CONFIG[6] offers a point of percussion alignment function
that maps the accelerometer sensors to the corner of the package
identified in Figure 21. To activate this feature, turn to Page 3
(DIN = 0x8003), then set GEN_CONFIG[6] = 1 (DIN =
0x8A40, 0x8B00. These example commands also disable the
linear-g compensation. To enable this function as well, use DIN =
0x8AC0, 0x8B00.
09389-021
PIN 1
PIN 23
POINT OF PERCUSSION
ALI GNME NT REFERE NCE P OI NT.
SEE GEN_CONFIG[6].
Figure 21. Point of Percussion Reference Point
